1. Field of the Invention
The present invention relates to an electron source and an image display device. In particular, the present invention relates to a method and apparatus for adjusting a characteristic of an electron source or image display device and a method and apparatus for manufacturing the electron source or image display device.
2. Related Background Art
Electron sources each comprising a plurality of electron emitting devices have been known. Image display apparatuses each comprising a plurality of display devices have also been known. Image display apparatuses have been known which use as display devices electron emitting devices (combined with fluorescent materials that emit light when irradiated with electrons) or electroluminescence devices.
Two types of electron emitting devices, that is, hot-cathode devices and cold-cathode devices have been known. The known cold-cathode devices include, for example, field emitting devices, metal/insulated layer/metal type emitting devices, and surface conduction type emitting devices.
The cold-cathode devices, the surface conduction type electron-emitting devices (hereinafter simply referred to as the xe2x80x9cdevicesxe2x80x9d) utilizes the phenomenon in which electrons are emitted by causing current to flow through a small-area thin film and parallel with its surface, the film being formed on a substrate and composed of SnO2, Au, In2O3/SnO2, carbon, or the like.
FIG. 15 shows an example of a typical device configuration. In this figure, reference numeral 3001 denotes a substrate, and reference numeral 3004 denotes a conductive thin film composed of a metal oxide and formed by sputtering. The conductive thin film 3004 is formed as an H-shaped plane as shown in the figure. The conductive thin film 3004 is subjected to a process called xe2x80x9cformingxe2x80x9d to form an electron emitting section 3005. The interval L in the figure is set between 0.5 and 1 mm, and the interval W therein is set at 0.1 mm. For the convenience of illustration, the electron emitting section 3005 is shown at the center of the conductive thin film 3004 to have a rectangular shape. However, this is schematic and does not faithfully represent the position or shape of the actual electron emitting section.
As described previously, to form an electron emitting section in a surface conduction type emitting device, current is allowed to flow through a conductive thin film to locally destroy, deform, or modify it to form a crack therein (forming process). Subsequently, an activation process can be executed to significantly improve an electron emitting characteristic.
That is, the activation process allows current to flow through the electron emitting section under appropriate conditions, the electron emitting section having been formed by a forming process, so that carbons or carbon compounds deposit in the vicinity of the electron emitting section. For example, in a vacuum atmosphere in which organisms under an appropriate pressure are present and which has a total pressure of 10xe2x88x922 to 10xe2x88x923 [Pa], by periodically applying pulses having a predetermined voltage, monocrystal graphite, polycrystal graphite, amorphous carbon, or a mixture thereof is deposited in the vicinity of the electron emitting section so as to have a thickness of about 500 Angstrom or less. However, these conditions are only an example and may be properly varied depending on the material or shape of the surface conduction type emitting device.
Such a process enables emitted current to be increased by a factor of 100 or more with the same applied voltage compared to a value measured immediately after forming. Accordingly, even when a multi-electron-source is manufactured which utilizes a large number of surface conduction type emitting devices such as those described above, each device is preferably subjected to the activation process. (After the activation process has been completed, the partial pressure on the organisms in the vacuum atmosphere is desirably reduced. This is called a xe2x80x9cstabilizing processxe2x80x9d.)
FIG. 16 shows a typical example of the emitted current Ie vs. device applied voltage Vf characteristic and device current If vs. device applied voltage Vf of a surface conduction type electron-emitting device.
The emitted current Ie is significantly smaller than the device current If, and it is thus difficult to illustrate it using the same scale. Further, these characteristics may be varied by varying design parameters such as the size and shape of the devices. Accordingly, the two graphs in the figure are shown in the respective arbitrary units.
The surface conduction type electron-emitting devices have the following three characteristics in connection with the emitted current Ie.
When a voltage equal to or larger than certain magnitude (this will be hereinafter referred to as a xe2x80x9cthreshold voltage Vthxe2x80x9d) is applied to the devices, they rapidly emit the emitted current Ie. On the other hand, with a voltage lower than the threshold voltage Vth, substantially no emitted current Ie is detected. That is, these are nonlinear devices having the definite threshold voltage Vth in connection with the emitted current Ie.
Since the emitted current Ie varies depending on the voltage Vf applied to the devices, the magnitude of the emitted current Ie can be controlled using the voltage Vf.
The current Ie emitted from the devices responds to the voltage Vf applied to the devices, at high speed, so that the amount of charges in electrons emitted from the devices can be controlled on the basis of the period of time for which the voltage Vf is applied.
In addition to the adjustment based on activation, the adjustment of the characteristics of the surface conduction type electron-emitting devices can be achieved by applying a voltage equal to or higher than a certain voltage (threshold voltage Vth) to the devices, that is, applying a characteristic shift voltage that adjusts the characteristics of the devices, as described in Japanese Patent Application Laid-Open No. 10-228867.
Further, since the surface conduction type electron-emitting devices have a simple structure and can be easily manufactured, they are advantageous in that a large number of devices can be formed over a large area. Thus, image forming apparatuses such as image display and recording apparatuses as well as electron beam sources have been researched to which the surface conduction type electron-emitting devices are applied.
The inventors have tested various surface conduction type electron-emitting devices that are composed of different materials, have different structures, and are manufactured using different methods. The inventors have also studied multi-electron-sources (simply referred to as xe2x80x9celectron sourcesxe2x80x9d) having a large number of surface conduction type electron-emitting devices arranged therein as well as image display apparatuses to which these electron sources have been applied.
For example, the inventors have tested an electron source based on the electrical wiring method shown in FIG. 17. In the figure, reference numeral 4001 denotes a schematically illustrated surface conduction type electron-emitting device, 4002 is a row-wise wire, and 4003 is a column-wise wire. In FIG. 17, reference numerals 4004 and 4005 denote wiring resistances.
The above described wiring method is called xe2x80x9csimple matrix wiringxe2x80x9d. For the convenience of illustration, a 6xc3x976 matrix is shown, but the scale of the matrix is not limited to this example.
In an electron source comprising devices connected together using the simple matrix wiring method, an appropriate electric signal is applied to the row-wise wires 4002 and the column-wise wires 4003. At the same time, a high voltage is applied to an anode (not shown).
For example, to drive arbitrary devices in the matrix, a selected voltage Vs is applied to the terminals of the row-wise wires 4002 for the selected rows, while, at the same time, a non-selected voltage Vns is applied to the terminals of the row-wise wires 4002 for the non-selected rows. Synchronously, modulation voltages Ve1 to Ve6 are applied to the terminals of the column-wise wires 4003 to output emitted current. With this method, the voltages Ve1xe2x88x92Vs to Ve6 are applied to the selected devices, while the voltages Ve1xe2x88x92Vns to Ve6 are applied to the non-selected devices. Emitted current of a desired intensity is output only from the selected devices by setting the voltages Ve1 to Ve6, Vs, and Vns at appropriate magnitudes so that a voltage equal to or higher than the threshold voltage Vth is applied to the selected devices, whereas a voltage lower than the threshold voltage Vth is applied to the non-selected devices.
Accordingly, the multi-electron-source comprising surface conduction type electron-emitting devices connected together using the simple matrix wiring method may be used for various applications. For example, the multi-electron-source is preferably used for an image display apparatus by properly applying an electric signal to this source, for example, in accordance with image information.
Further, in addition to the surface conduction type electron-emitting devices, electron emitting devices called xe2x80x9cspindt type electron emitting devicesxe2x80x9d are known which each comprise projecting emitters (emitter cones) and gate electrodes located in proximity thereto. Also in the spindt type electron emitting device, after an emitter and a gate has been constructed, the electron emitting characteristic of the device can be adjusted by applying a voltage between the emitter and the gate. It is also known that the characteristic of an electroluminescence device varies depending on a voltage or heat applied to the device.
For display devices such as electron emitting devices, a characteristic (for example, in the case of electron emitting devices, the electron emission characteristic) of the individual devices may vary slightly. If these devices are used to produce a display apparatus, then this variation in characteristic results in a variation in luminance. Japanese Patent Application Laid-Open No. 10-228867 and other publications use a step of reducing this variation.
The causes of the different electron emission characteristics of the electron emitting devices of an electron source include, for example, a variation in the components of a material used for the electron emitting section, an error in the size or shape of each member of the device, non-uniform conduction conditions for a conductive forming process, and non-uniform conduction conditions or atmospheric gases for an conductive activation process. However, elimination of all these causes requires a very advanced manufacture facility and very rigorous process management, and enormous costs are required to meet these requirements.
This is also applicable to the use of electron emitting devices other than the surface conduction type electron-emitting devices or display devices other than the electron emitting devices.
The inventors have made wholehearted efforts to find that in particular non-uniform display is significantly perceived if this variation has a high-frequency component. Thus, the inventors have concluded that a target value for a change in characteristics should be set so as to reduce, in particular, high-frequency components of the spatial distribution of a variation in characteristics.
An aspect of the invention according to present application is constructed as follows:
That is, the present invention provides a method of adjusting a characteristic of an electron source having a plurality of electron emitting devices arranged on a substrate, the method being characterized by comprising:
a characteristic changing step of changing electron emission characteristics of the electron emitting devices, and
in that in the characteristic changing step, target values indicative of targets for changes in electron emission characteristic are such that a spatial distribution of the target values has spatial frequencies obtained by removing predetermined high-frequency components from spatial frequencies of a spatial distribution of the electron emission characteristics of the plurality of electron emitting devices obtained before the characteristic changing step or reducing predetermined high-frequency components of the spatial distribution, and in the characteristic changing step, the electron emission characteristics are changed so as to approach the respective target values.
The spatial distribution of the electron emission characteristics of the electron emitting devices is obtained by plotting the electron emission characteristics of the plurality of electron emitting devices in association with the positions of the electron emitting devices. In this case, when the plurality of electron emitting devices are linearly arranged, a line extending along the direction in which the devices are arranged is defined as an X axis, and a spatial distribution is obtained by showing data indicative of the electron emission characteristics of the devices in the direction of a Z axis. When the electron emitting devices are two-dimensionally arranged, the plane on which the devices are arranged is defined as an XY plane, and a spatial distribution is obtained by showing the electron emission characteristics in the direction of the Z axis depending on the positions of the devices. This is also applicable to the space distribution of the target values, and the spatial distribution is obtained by plotting the target values for the plurality of electron emitting devices in association with the positions of the electron emitting devices.
To set the spatial distribution of the target values to contain the spatial frequencies obtained by removing the predetermined high-frequency components from the spatial frequencies of the spatial distribution of the electron emission characteristics of the plurality of electron emitting devices obtained before the characteristic changing step or reducing the predetermined high-frequency components of the spatial distribution, the following filtering step is preferably executed: the spatial distribution of the electron emission characteristics of the plurality of electron emitting devices obtained before the characteristic changing step is converted into spatial frequencies, and subsequently the predetermined high-frequency components are removed from the spatial frequencies obtained or the ratio of the predetermined high-frequency components to the spatial frequencies is reduced, and then the resulting spatial frequencies are converted into a spatial distribution for target values. The conditions in the present invention are met if the spatial distribution of target values obtained by another method, for example, polynominal approximation, described later, or target values obtained by using another filtering method for-instance a convolution operation to smooth a spatial distribution without converting it into spatial frequencies has resultingly spatial frequencies obtained by removing predetermined high-frequency components from the spatial frequencies of the spatial distribution of the electron emission characteristics of the plurality of electron emitting devices obtained before the characteristic changing step or reducing predetermined high-frequency components of the spatial distribution.
In the context of the specification, the predetermined high frequency components means xe2x80x9ccomponentsxe2x80x9d which appear as disadvantageous variations for electron emission characteristics or display characteristics, for instance a visually harmful variation in a displayed image, if the variation has some amplitude (magnitude). What is meant by these predetermined high frequency components depend area size in arrangement of electron emission devices, space between electron emission devices in the electron source or display apparatus and etc. One way of determining the predetermined high frequency components is based on experiments. A plurality of electron sources and display apparatus are actually fabricated. The electron emission characteristics and display characteristics on them are measured and then characteristics adjustments on them are performed with taking different predetermined high frequency components for respective electron sources or display apparatus. That is, high frequency components to be removed are determined by evaluating the electron source and display apparatus according to their usages (for example, the degree of incongruity is evaluated by actually displaying an image in the apparatus). The target vales shall be set to reduce the disadvantageous characteristics variations due to predetermined the high frequency components. It takes a lot of time to adjust the characteristics of all the devices to the same target value. Instead, it is advantageous to determine the spatial distribution of target values comprising low frequency components which roughly reflects the characteristics of the devices measured before taking the changing step (at the pre-changing). In other words, the predetermined high frequency components are at least part of components higher in frequency than the low frequencies of components which roughly reflect the characteristics distribution of the devices measured before taking the changing step. Even if the spatial distribution of the characteristics has the predetermined high frequency components in the above context, a small amplitude of variation appearing at those high frequencies is tolerable. It is not necessarily required to completely clear the predetermined high frequency components. It is one way to determine the target values so that the amplitude (magnitude) of variation of the predetermined high frequency components is reduced. When the amplitude (magnitude) of variation of high frequency components which are regarded harmful is tolerably small without the changing step, it is another way to determine the target values so that the variations of these high frequency components remains as it is.
Further, the spatial distribution of the target values has spatial frequencies and is thus not uniform. This means that the target values for changes in the characteristics of all the devices are not set the same value. If for example, the plurality of electron emitting devices are linearly arranged, when the direction in which the devices are arranged is defined as the X axis and the target values are shown on the Z axis, the line formed by the target values on the XZ plane is not a straight line with a zero inclination. Preferably, this line is a straight line with a non-zero inclination (Z=pX where p is a constant) or a curve represented as function of X with a Z item having the second or later order, that is, a function including an item with the second or later power of X. If the plurality of electron emitting devices are two-dimensionally arranged, when the devices are arranged on the XY plane and the target values are shown on the Z axis, the surface formed by the target values is not a plane with a zero inclination. Preferably, this surface is a plane with a non-zero inclination or a curved surface.
The present application includes the following aspect of the invention:
That is, the present invention provides a method of adjusting a characteristic of an electron source having a plurality of electron emitting devices arranged on a substrate, the method being characterized by comprising:
a characteristic changing step of changing electron emission characteristics of the electron emitting devices, and
in that in the character changing step, target values indicative of targets for changes in electron emission characteristics have a non-uniform spatial distribution, and the spatial distribution is obtained by an step of reducing predetermined high-frequency components of spatial frequencies of a spatial distribution of the electron emission characteristics of the plurality of electron emission characteristics obtained before the character changing step, and in the character changing step, the electron emission characteristics are changed so as to approach the respective target values.
Another aspect of the invention according to the present application provides a method of adjusting a characteristic of an electron source having a plurality of electron emitting devices arranged on a substrate, the method being characterized by comprising:
a characteristic changing step of changing electron emission characteristics of the display devices, and
in that in the character changing step, target values indicative of targets for changes in electron emission characteristics have a non-uniform spatial distribution, and the spatial distribution is obtained by an step of smoothing the spatial distribution of the electron emission characteristics of the plurality of electron emitting devices obtained before the character changing step, and in the character changing step, the electron emission characteristics are changed so as to approach the respective target values.
Also in this aspect, the spatial distribution of the target values preferably constitutes a straight line or curve with a non-zero inclination, or a plane or curved surface with a non-zero inclination.
In the above described aspects of the invention, the operation of changing the electron emission characteristics in the character changing step preferably changes the amount of electrons emitted when a predetermined voltage is applied to the electron emitting devices.
Further, the target values are preferably obtained by subjecting the spatial distribution of the electron emission characteristics of the plurality of electron emitting devices to Fourier transform, removing predetermined high-frequency components from the resulting of the Fourier transform, and subjecting the resulting spatial frequencies to inverse Fourier transform. That is, a filtering process is executed by converting a spatial distribution into spatial frequencies.
Further, the target values are preferably obtained by subjecting the spatial distribution of the electron emission characteristics of the plurality of electron emitting devices obtained before the character changing step, to polynominal approximation to obtain an equation of a predetermined order equal to or later than the first order. This is a filter processing by use of polynominal approximating wherein some order terms among terms x0, x1, x2 . . . xn corresponding to high frequency components to be removed are deleted in the approximated polynominal equation.
Furthermore, the target values are preferably obtained by smoothing the spatial distribution of the electron emission characteristics of the plurality of electron emitting devices obtained before the character changing step. This smoothing is preferably achieved by a convolution operation for example.
Moreover, the method preferably comprises a step of determining the target values, the target value determining step having a high-frequency component reducing step of removing predetermined high-frequency components from the spatial distribution of the electron emission characteristics of the plurality of electron emitting devices obtained before the character changing step or reducing high-frequency components of the spatial distribution, and a step of offsetting the spatial distribution obtained in the high-frequency component reducing step while maintaining the shape of the spatial distribution. If the characteristics of the electron emitting devices can change in only one direction and if some of the devices have characteristics larger than the target values while the others have characteristics smaller than the target values, then either group of devices cannot have their characteristics changed. In this case, the target values can be moved upward or downward with the shape of the spatial distribution maintained to reduce the number of devices the characteristics of which cannot be changed. The high-frequency component reducing step of removing the predetermined high-frequency components from the spatial distribution of the electron emission characteristics of the plurality of electron emitting devices obtained before the character changing step or reducing the high-frequency components of the spatial distribution can be achieved by converting the spatial distribution into spatial frequencies and filtering the spatial frequencies obtained or smoothing (filtering) the spatial distribution without a conversion into spatial frequencies.
Further, the characteristics are preferably changed by applying a voltage to the electron emitting devices. In particular, electrons are emitted from the electron emitting devices by applying a voltage to between electrodes, and the characteristics are preferably changed by applying a voltage to between the electrodes.
Furthermore, the spatial distribution of the electron emission characteristics is obtained by executing a step of measuring the electron emission characteristics of the plurality of electron emitting devices before the characteristic changing step.
Moreover, a measuring step of measuring the electron emission characteristics, a target value determining step of determining the target values, and a step of changing the electron emission characteristics can be executed for each group of electron emitting devices of the plurality of electron emitting devices.
The method preferably comprises a measuring step of measuring the electron emission characteristics of some of the plurality of electron emitting devices, a target value determining step of determining the target values for those of the plurality of electron emitting devices which have the electron emission characteristics measured in the measuring step, and a step of changing the electron emission characteristics of those of the plurality of electron emitting devices which have the electron emission characteristics measured in the measuring step. In particular, the method comprises a further measuring step of measuring the electron emission characteristics of the plurality of electron emitting devices other than those which have the electron emission characteristics measured in the measuring step, and a further changing step of changing the electron emission characteristics of the electron emitting devices that have the electron emission characteristics measured in the further measuring step, wherein in the further changing step, target values indicative of targets for changes in electron emission characteristics are determined on the basis of results of measurements in the further measuring step and results of measurements in the measuring step. With this configuration, if the characteristics are changed for each small area, they are prevented from being discontinuous at the boundary between small areas.
The electron emission characteristics of the electron emitting devices may be changed in various manners depending on the applied electron emitting devices, but the changing operation is preferably performed in an atmosphere in which the changed electron emission characteristics can be maintained. For example, when the electron emission characteristics of the electron emitting devices are changed in an atmosphere in which an organic gas undergoes a partial pressure of 1.0xc3x9710xe2x88x926 [Pa] or lower, deposits associated with the organic gas are prevented from depositing on the electron emitting devices, thereby allowing the changed characteristics to be easily maintained.
Further, the above described characteristic adjusting method can be executed with appropriate timings. For example, the above described characteristic adjustment may be carried out as required after normal driving for a while. Alternatively, it may be executed as part of a manufacture process.
The present invention includes the following method of adjusting a characteristic of an electron source having a plurality of electron emitting devices, the method comprising a characteristic changing step of changing electron emission characteristics of the electron emitting devices,
wherein in the characteristic changing step, target values indication of targets for changes in electron emission characteristics are determined by reflecting a spatial distribution of electron emission characteristics of the electron emitting devices taken before the characteristic changing step on a spatial distribution of the target values whereby the total amount of the electron emission characteristic changes is less than the total amount of electron emission characteristic changes by which electron emission characteristics of all of the electron emitting devices become identical, and the electron emission characteristics are changed to approach to the respective target values.
By setting the target values so that the spatial distribution of the target values reflect the spatial distribution of the characteristics (in pre-changing) of the devices, the total amount of the characteristic changes (sum of characteristics changes performed on the respective devices) can be less than the total amount of characteristic changes by which characteristics of all of the electron emitting devices become uniform. It is preferable to roughly reflect the spatial distribution of the characteristics in pre-changing on the spatial distribution of the target values.
Furthermore, the present invention is not limited to electron sources having electron emitting devices, but is applicable to image display apparatuses using electron emitting devices as image display devices or display devices (for example, electroluminescence devices) other than the electron emitting devices.
That is, the present invention provides a method of adjusting a characteristic of an image display apparatus having a plurality of display devices, the method being characterized by comprising:
a characteristic changing step of changing electron emission characteristics of the display devices, and
in that in the characteristic changing step, target values indicative of targets for changes in display characteristic are such that a spatial distribution of the target values has spatial frequencies obtained by removing predetermined high-frequency components from spatial frequencies of a spatial distribution of the display characteristics of the plurality of display devices obtained before the characteristic changing step or reducing predetermined high-frequency components of the spatial distribution, and in the characteristic changing step, the display characteristics are changed so as to approach the respective target values.
Another aspect of the invention according to the present application provides a method of adjusting a characteristic of an image display apparatus having a plurality of display devices, the method being characterized by comprising:
a characteristic changing step of changing display characteristics of the display devices, and
in that in the character changing step, target values indicative of targets for changes in display characteristics have a non-uniform spatial distribution, and the spatial distribution is obtained by an step of reducing predetermined high-frequency components of spatial frequencies of a spatial distribution of the display characteristics of the plurality of display characteristics obtained before the character changing step, and in the character changing step, the display characteristics are changed so as to approach the respective target values.
Another aspect of the invention according to the present application provides a method of adjusting a characteristic of an image display apparatus having a plurality of display devices, the method being characterized by comprising:
a characteristic changing step of changing display characteristics of the display devices, and
in that in the character changing step, target values indicative of targets for changes in display characteristics have a non-uniform spatial distribution, and the spatial distribution is obtained by an step of smoothing the spatial distribution of the display characteristics of the plurality of display devices obtained before the character changing step, and in the character changing step, the display characteristics are changed so as to approach the respective target values.
Additionally, the present invention includes a method of adjusting a characteristic of an image display apparatus having a plurality of image display devices, the method comprising:
A characteristic changing step of changing display characteristics of the image display devices,
wherein in the characteristic changing step, target values indicative of targets for changes in display characteristics are determined by reflecting a spatial distribution of display characteristics of the electron emitting devices taken before the characteristic changing step on a spatial distribution of the target values whereby the total amount of the display characteristic changes is less than the total amount of display characteristic changes by which display characteristics of all of the image display devices become identical, and the display characteristics are changed to approach to the respective target values.
In this case, the operation of changing the display characteristics in the characteristic changing step preferably changes a luminance obtained when a predetermined voltage is applied to the display devices.
The aspect of the invention which has been described in conjunction with adjustment of a characteristic of an electron source is also applicable to adjustment of a characteristic of an image display apparatus, and still constitutes the invention according to the present application.